"...it was a blow, to be shown himself as alien as a castaway from Mars."
-Poul Anderson, Murder In Black Letter, Chapter 13.
"...alien..." and "...from Mars..." might remind us that:
Anderson is primarily an sf writer;
the idea of Martians exists in the minds of characters even in a contemporary novel;
even though such a novel usually avoids references to anything beyond Earth's atmosphere, the cosmic context of all life remains in the background. See here.